The dynamic mechanical behavior of a poly(ethylene-co-methacrylic acid) polymer containing 4.1 mo! % methacrylic acid groups and its sodium, lithium and calcium salts was studied at llO Hz in the tem­perature range -180 to -60°. It was found that the 'Y relaxation occurring in this region consists of two over­lapping peaks. It is shown that the low-temperature peak, occurring at -163 °, arises in the crystalline phase, while the high-temperature peak, occurring at -129°, arises in the amorphous phase. It is proposed that the motion responsible for the -163 ° peak arises around defect points in the crystal. It is further shown that the carboxylic acid groups or salt groups, which are entirely present in the amorphous phase, do not take part in the molecular motion responsible for the 129° peak. It is thus concluded that the amorphous relaxation is due to local motions of polyethylene segments.